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the germans and austrians must reload
- Thread starter pelo801
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JohnKSa said:Slide velocity is affected by a number of variables, the primary ones being the weight of the recoiling mass (slide/barrel combination in the case of a typical locked breech semi-auto pistol) and the muzzle momentum of the load being shot. The recoil spring must have some effect since it exerts a force opposite the recoil momentum. Exactly how much effect it has depends on the design of the firearm the strength of the recoil spring, how much compression it's under when installed, etc.
Yes, of course it has some effect, just like hitting a bug with my windshield has some effect in slowing down my car.
Consider the forces on the breech during bullet acceleration. A .45 ACP has a standard pressure of 21,000 psi. The base of a .452 diameter bullet has 0.16 square inches of area. 21,000 pounds/square inch X 0.16 square inch = 3360 pounds of force on the base of the bullet and exactly 3360 pounds of force exerted backwards on the breech. A spring strong enough to significantly interfere with the rearward acceleration of the slide and barrel during bullet acceleration would be so strong that Rambo couldn't pull the slide back to cock the gun.
What the spring does is absorb the kinetic energy of the slide as the slide moves backwards after the pressure is gone. The problem is, a spring that absorbs energy during compression also gives that energy back when it decompresses, so a spring that's strong enough to totally prevent the rearward hammering as the slide reaches its stop will hammer the slide as the breech closes again, perhaps hard enough to cause the inertia of the firing pin to slam-fire the round.
Unless, we can invent a 20 pound spring that magically becomes a 5 pound spring when it returns the slide.
Mike Irwin
Staff
All I know regarding the spring issue is that when I dropped a Wolff 22 pound spring into my Witness it stopped throwing the cases into the next time zone and started depositing them between 10 and 15 feet away.
I'm sure there's some mathematical formula to explain it, probably involving square pies and other assorted tasty pastries. But I was more intereted in the fact that I was no longer losing upwards half my expensive 10mm brass.
I'm sure there's some mathematical formula to explain it, probably involving square pies and other assorted tasty pastries. But I was more intereted in the fact that I was no longer losing upwards half my expensive 10mm brass.
Last week I finished up a Sig LE Classic P series armorers course. This was covered in quite a fair amount of detail. In fact, it is pretty much the basis of how and why the Sig P229 and heavier one-piece slide came into being. The old 228 and two piece (stamp sheet, breech block, and weld) slides were getting beaten to death when it started looking like Sig needed to field a .40 S&W, 10mm, and the other ctg in contention for the FBI trials. And curiously, it's why the recommended LE service life of the recoil springs are 3yrs/5,000 miles... er, rounds- to preserve the life and integrity of the frames.Slide velocity is affected by a number of variables, the primary ones being the weight of the recoiling mass (slide/barrel combination in the case of a typical locked breech semi-auto pistol) and the muzzle momentum of the load being shot. The recoil spring must have some effect since it exerts a force opposite the recoil momentum. Exactly how much effect it has depends on the design of the firearm the strength of the recoil spring, how much compression it's under when installed, etc.
Good call.
just to clarify a little, it was my glock 20 that i was shooting, with hotter hand loads. the witness was with some run of the mill american eagle. and you revolver guys sure are clever. but i have noticed i really like shooting 38 spcl more and more lately. i just might look into a new spring for the witness and see how that goes.
Shadi Khalil
New member
My 239 will spit brass in the same spot every time as long as I do my part.
John Bercowitz did a simplified assessment of the physics of a 1911's operation and determined that the recoil spring soaked up about 20% of the slide's remaining energy after the barrel/slide unlock.Yes, of course it has some effect, just like hitting a bug with my windshield has some effect in slowing down my car.
http://yarchive.net/gun/pistol/1911_dynamics.html
It's safe to say that his number is low because he doesn't take into account any of the energy used up in extracting and ejecting the empty case.
All I'm trying to say is that the forces involved with accelerating the slide before barrel unlock are so strong that the spring has little effect on it. Once the bullet clears the barrel, before the slide even unlocks, everything is just coasting on momentum, that's when the spring does its work.
The slide's kinetic energy has to go somewhere and springs don't use up kinetic energy, they convert kinetic energy into potential energy and then when the slide closes, they convert that potential energy back into kinetic energy. If the spring was sized to use up 100% of the slide's kinetic energy, you would have a slide that hammered the gun when it closed instead of when it opened.
One way to get rid of kinetic energy is to give it to the empty case, hence guns that throw empty cases into the next zip code.
The slide's kinetic energy has to go somewhere and springs don't use up kinetic energy, they convert kinetic energy into potential energy and then when the slide closes, they convert that potential energy back into kinetic energy. If the spring was sized to use up 100% of the slide's kinetic energy, you would have a slide that hammered the gun when it closed instead of when it opened.
One way to get rid of kinetic energy is to give it to the empty case, hence guns that throw empty cases into the next zip code.
Interesting discussion on the topic and physics behind it all. I can't say my Glock Gen3 G22 spits 'em out in a neat pile. It throws 'em 20-30 feet to the right and back about 3-6 o'clock. Been wondering what the difference is between the Gen3 and Gen4 recoil spring assemblies is and if a Gen4 assembly would remedy the long distance ejection so I don't lose so darn many of the buggers...
Tapatalked via my highly abused iPhone
Tapatalked via my highly abused iPhone
As far as the springs go, I think both sides of the argument have some merit. Springs apply a stronger force as they're compressed, so at the beginning of the slides movement they won't be providing as much resistance, but as the slide moves back the spring pushes harder - I presume the "22lbs" would be an average of the force over the springs intended travel.
So, the rearward velocity of the slide wouldn't be effected as much at the front of it's travel than at the rear. However, if stronger springs fix the problem, clearly the velocity must still be effected. How much exactly would make for an interesting physics problem.
As far as the trajectories of my cases, none come back at me, and as I don't reload that's all I really ask for.
So, the rearward velocity of the slide wouldn't be effected as much at the front of it's travel than at the rear. However, if stronger springs fix the problem, clearly the velocity must still be effected. How much exactly would make for an interesting physics problem.
As far as the trajectories of my cases, none come back at me, and as I don't reload that's all I really ask for.
Run through Bercowitz' analysis. It's quite good. You'll see that the spring absorbs about 20% of the slide's remaining kinetic energy after the barrel unlocks. Since that's the portion of slide travel that extracts and ejects the cartridge, it is certainly applicable to this discussion.All I'm trying to say is that the forces involved with accelerating the slide before barrel unlock are so strong that the spring has little effect on it.
The recoil spring is not a huge effect, but it is a significant effect and one that can not be discounted.
By the way, you can get confused looking at the forces. The force applied to the breech accelerates the slide/barrel combination to about 25fps over the space of about 6 tenths of a millisecond. That's impressive, but 25fps isn't scary fast or anything nor does the slide/barrel combination have an imposing amount of kinetic energy after that acceleration process. Basically it takes a huge amount of force to get a stationary object weighing about a pound moving that fast because there is only an infinitesimally short amount of time to do the job.
Recoil springs certainly do absorb kinetic energy. They absorb it and store it as potential energy when they are compressed and then convert it back to kinetic energy when they are allowed to decompress. That's pretty basic physics. Bercowitz' analysis makes this plain as well, and is fairly readable.The slide's kinetic energy has to go somewhere and springs don't use up kinetic energy,
One way to get rid of kinetic energy is to give it to the empty case, hence guns that throw empty cases into the next zip code.
From a number of sources (and my own calculations) it turns out that the slide velocity on a typical 1911 pistol is about 25fps.
I calculated the amount of force required to accelerate the slide/barrel combination to 25fps during the time the bullet is in the barrel (5 or 6 tenths of a millisecond). Interestingly enough, it comes out much lower (almost 2/3 lower) than the total force applied to the breechface based on the pressure & force relationship. That means that nearly 2/3 of the force applied to the breechface is NOT being used to accelerate the slide/barrel combination to 25fps. Said another way, you don't need nearly 3400 something lbs of force to get the slide moving that fast, only about 1400 something lbs of force is all you need. My best guess is that extra force applied (3400-1400lbs force) is used up extracting and ejecting the case.
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JohnKSa said:Ok, here's an interesting exercise. I'd be interested to see if you get the same results I did.
From a number of sources (and my own calculations) it turns out that the slide velocity on a typical 1911 pistol is about 25fps.
I calculated the amount of force required to accelerate the slide/barrel combination to 25fps during the time the bullet is in the barrel (5 or 6 tenths of a millisecond). Interestingly enough, it comes out much lower (almost 2/3 lower) than the total force applied to the breechface based on the pressure & force relationship. That means that nearly 2/3 of the force applied to the breechface is NOT being used to accelerate the slide/barrel combination to 25fps. Said another way, you don't need nearly 3400 something lbs of force to get the slide moving that fast, only about 1400 something lbs of force is all you need. My best guess is that extra force applied (3400-1400lbs force) is used up extracting and ejecting the case.
I have a simpler explanation. The average pressure during bullet acceleration is much lower than the peak pressure.
Let's take a hypothetical 4 inch barrel, I choose 4 inches only because that's exactly 1/3 of a foot, makes the math simple, OK make that 4 inches plus the chamber.
If the powder was able to maintain 21000 psi on the base of the bullet for the entire trip down the barrel, applying 3400 pounds of force on the base of the bullet for 1/3 foot of travel, then it would be doing 3400/3 or 1133 ft lb of work on the bullet and thus the bullet would have 1133 ft lb of kinetic energy at the muzzle. Also, the gun would be earsplitting loud when the bullet suddenly uncorked that 21000psi of pressure.
Since real .45ACP rounds don't come close to that energy, even in 16 inch carbines, it's obvious that the pressure drops off rapidly as the bullet travels down the bore.
That is exactly correct. I was thinking about it this morning and realized that I had calculated the average force and compared it to the peak force.I have a simpler explanation. The average pressure during bullet acceleration is much lower than the peak pressure.
RedBowTies88
New member
My p64 ejects brass with such vigor it actually hit a friend of mine in the head and gave him a half moon shapped cut on his forehead.
also my saiga in .223 launches the casings way to far away to begin to try and find.
also my saiga in .223 launches the casings way to far away to begin to try and find.
Mike Irwin
Staff
"it's obvious that the pressure drops off rapidly as the bullet travels down the bore."
Very much so.
Around the time I was working for American Rifleman there was an article on bore pressures in one of the magazines we got in our library. Can't remember which one it was, but it put one of the manufacturer's (Ohler, IIRC, it was I think an early version of the System 83 Ballistics Instrumentation set up that they offer) computerized chronograph setups to use.
It used strain gauges glued to the breech of the gun and hooked into a computer, and would provide a neat pressure over time graph.
Peak pressure occurs pretty early in the firing cycle and it drops very rapidly after that.
Very much so.
Around the time I was working for American Rifleman there was an article on bore pressures in one of the magazines we got in our library. Can't remember which one it was, but it put one of the manufacturer's (Ohler, IIRC, it was I think an early version of the System 83 Ballistics Instrumentation set up that they offer) computerized chronograph setups to use.
It used strain gauges glued to the breech of the gun and hooked into a computer, and would provide a neat pressure over time graph.
Peak pressure occurs pretty early in the firing cycle and it drops very rapidly after that.
Crow Hunter
New member
Pressure is a Force/Area.
The pressure at the moment of ignition is in a very small volume (case in the chamber) and therefore a smaller surface area so it is at a very large pressure.
As the bullet travels down the bore, the volume behind the bullet gets larger, thus the surface area acted on by the pressure gets larger. The force is now distributed over a greater surface area in the, so the pressure will go down.
That is why we don't get the effect that BLE was referring to.
The pressure at the moment of ignition is in a very small volume (case in the chamber) and therefore a smaller surface area so it is at a very large pressure.
As the bullet travels down the bore, the volume behind the bullet gets larger, thus the surface area acted on by the pressure gets larger. The force is now distributed over a greater surface area in the, so the pressure will go down.
That is why we don't get the effect that BLE was referring to.
warningshot
New member
I suppose one could always use reduced loads to intentionally produce stovepipes with every shot; that way you could just wipe off each spent brass after each firing.